In carrying out ethanol production using cellulosic biomass as the feedstock, first the biomass is degraded to monosaccharides and the saccharified solution is used as the substrate for fermentation. Degradation and saccharification of cellulosic biomass are carried out by enzyme process using cellulase or acid saccharification process using sulfuric acid or the like. Whereas, because certain biomasses have high hemicellulose contents besides those of cellulose, their saccharified solutions may contain, besides glucose, hemicellulose-derived xylose. Representative microorganisms used for ethanol production are yeast belonging to genus Saccharomyces or bacteria belonging to genus Zymomonas or Zymobacter. These microorganisms normally produce ethanol efficiently from sugars such as glucose, but are incapable of producing ethanol from xylose. To improve yield in ethanol production from biomass feedstock, therefore, it is necessary to construct a transformed microorganism capable of producing ethanol from xylose substrate, by introducing an enzyme which participates in xylose metabolism into said microorganisms used for ethanol production.
Bacteria of genus Zymomonas and genus Zymobacter are known to show higher fermentation speed than yeast of genus Saccharomyces. For example, U.S. Pat. No. 5,712,133 has disclosed construction of transformed microorganisms which could efficiently produce ethanol from xylose, by transforming Zymomonas bacteria to impart thereto pentose fermentation ability. Zymomonas bacteria, however, have narrower fermentable sugar range than Zymobacter bacteria, and must be transformed with still more genes for fermenting feedstocks comprising maltose, galactose, mannose and the like with high efficiency.